This invention relates generally to an analgesic apparatus and, more particularly, to a gas flow control system for analgesic apparatus of the continuous flow type.
Continuous flow type analgesic machines are widely used today in conjunction with a breathing circuit to provide a complete analgesic system. These machines blend or mix a gaseous analgesic with oxygen in proportional amounts to produce a gaseous mixture having a desired analgesic concentration. Conventionally, such machines utilize individual control valves associated with individual flow meters to separately control the flow of each gas in order to obtain the desired oxygen concentration at the required total flow rate. Such arrangements sometimes provide a minimum oxygen flow at all times and a maximum flow of analgesic gas to ensure a minimum dilution of the analgesic gas. When it becomes necessary to either adjust the oxygen concentration while maintaining the total flow rate constant or adjust the total flow rate without varying the oxygen concentration each of the control valves must be adjusted and a computation performed to determine the flow rate required of each gaseous component to maintain the desired total flow rate. It also is known to provide a control for varying the flow rates of both components without varying the total flow rate. It is desirable to be able to limit the relative proportions of the components without requiring a minimum flow of oxygen and a maximum flow of analgesic gas while permitting the adjustment of the total flow rate without varying the relative proportions previously selected.